The present invention relates to a non-contact charging equipment for transmitting electric power from a charger to a battery on non-contact basis by electromagnetic induction, and in particular to a non-contact charging equipment for efficiently transmitting electric power.
Charging to a secondary battery to be used as power source for portable devices has been generally performed by transmitting electric power through conductive contact between metallic contact and contact of a charger on a battery pack or on a battery pack mounted on a device.
However, there have been problems in that poor conductive contact occurs or charging cannot be achieved due to oxidation of the metal of the contact or due to attachment of dust or oil, and abnormal heating occurs at the contact. Also, accidents are sometimes caused by electrostatic destruction of electronic components inside the device due to contact of metal contact with human body or other electrically charged object.
Further, there have been problems such as complicated structure of the equipment because waterproof construction must be adopted when conductive contact is provided on the surface of the equipment.
To solve the above problems, there has been proposed a method to supply electric power from the transmitting side to the receiving side using electromagnetic induction between coils provided on both the power transmitting side and the power receiving side, thus without replying on conductive connection through contacts.
In a transmission equipment of charging current using electromagnetic induction, coils wound on a core such as ferrite core have been used. However, transmission efficiency is lower despite of large volume and heavy weight of the equipment, and output is about 2 W and there is also problem of heating.
To overcome these problems, an equipment having high transmission efficiency combining a magnetically soft material and a flat-faced spiral coil has been proposed instead of the coil wound on ferrite core, and this is described as a cordless power station in JP-A-7-231586.
However, even in this type of equipment, battery is sometimes arranged away from the coil on the power receiving side, and the measures to prevent excessive heating caused by coil have also been not very satisfactory.
In particular, it is generally practiced to use metal such as iron or its alloy as a battery can, and it is necessary to arrange the battery away from magnetic line of force for receiving electric power. Specifically, when it is desired to increase electric power for charging, magnetic force on the power transmitting side is also increased. As a result, large space is required on the side of the portable device, and it is considered as difficult to arrange it in a battery pack.
It is an object of the present invention to provide a non-contact charging equipment for supplying electric power from power transmitting side to power receiving side on non-contact basis by electromagnetic induction, by which it is possible to transmit and receive electric power efficiently and to suppress heating, and also to provide an equipment where the equipment on the power receiving side is arranged in a battery pack.